Make testInteractions compile with PE-SPH.

tests/testInteractions.c

@@ -110,7 +110,12 @@ void dump_indv_particle_fields(char *fileName, struct part *p) {
           "%13e %13e %13e %13e "
           "%13e %13e %13e %10f\n",
           p->id, p->x[0], p->x[1], p->x[2], p->v[0], p->v[1], p->v[2],
-          p->a_hydro[0], p->a_hydro[1], p->a_hydro[2], p->rho, p->rho_dh,
+          p->a_hydro[0], p->a_hydro[1], p->a_hydro[2], p->rho,
+#ifdef HOPKINS_PE_SPH
+          p->density.rho_dh,
+#else
+          p->rho_dh,
+#endif
           p->density.wcount, p->density.wcount_dh, p->force.h_dt,
           p->force.v_sig,
 #if defined(GADGET2_SPH)